In a liquid crystal display, a state of a molecular alignment of a liquid crystal is changed by an action of electric field so as to utilize a change in optical characteristics involved in the action for display. Mostly, the liquid crystal is used in the state of being sandwitched by two substrates. The inside of substrates is subjected to an aligning treatment so as to align liquid crystal molecules to a specific direction.
Usually, a rubbing method, which includes the steps of providing a polymer film made of polyimide on a substrate made of a glass and rubbing with a cloth in one direction, is used in the aligning treatment. Consequently, liquid crystal molecules, which are in contact with the substrate, are aligned so that the major axis (director) is parallel to the rubbing direction. Although the rubbing method has an advantage in that a production apparatus is simple, alignment defects are caused by scratch or dust on the surface of an alignment film in the production processes, and thus an adverse influence may be exerted on the resulting display characteristics. In a TFT type liquid crystal cell which has often been used, recently, a TFT element provided preliminarily on a substrate is broken by static electricity generated in the rubbing process, which results in decrease of the yield on production.
To the contrary, an intense interest has recently shown towards a technique for controlling a photo-alignment film without rubbing. Particularly, a photo-aligning method, which includes the step of irradiating a coating film provided on a substrate with polarized light to cause liquid crystal alignment, has intensively been studied because of simpleness. As the photo-aligning method, for example, a method by means of photoisomerization or rearrangement of a photo-aligning group capable of exerting a photo-aligning function in an organic molecule, for example, an azo group; a method by means of photodimerization of a cinnamoyl group, a cumarin group, or a chalcone group; a method by means of photocrosslinking of a benzophenone group; and a method by means of photolysis of a polyimide resin have been proposed.
Among these photo-aligning methods, a method utilizing azobenzene is attractive because high sensitivity and high alignment-regulating force is obtained. For example, a method, which includes the step of irradiating an azo compound represented by the formula (A) with light having anisotropy thereby producing a photo-alignment film, is known (for example, see non-patent reference 1). Also, there is known an azo compound represented by the formula (B) in which a polymerizable functional group is included in an azo compound for the purpose of stabilizing an alignment state of these photo-aligning groups (for example, see patent reference 1).

The patent reference 1 discloses a method including the steps of coating a composition for photo-alignment film containing a dichromatic dye having one or more polymerizable functional groups in a molecule on a substrate, irradiating the coated substrate with polarized light thereby imparting a liquid crystal aligning function, and polymerizing the polymerizable functional groups through heating or light irradiation to obtain a photo-alignment film. The dichromatic dye is low molecular and can be simply aligned, and also it has two or more polymerizable functional group and can be easily polymerized, and thus a photo-alignment film having excellent long-term stability can be provided.
However, the liquid crystal device using the photoalignment film obtained by the method had a problem such as a low voltage-holding ratio. It is necessary to hold the applied voltage until the following writing in a TFT type liquid crystal cell, and a problem such as flickering of a screen arises when the voltage-holding ratio is low. Therefore, it is an important object to improve the voltage-holding ratio so as to put a photo-alignment film into practical use.    [Non-patent reference 1] Molecular Crystals and Liquid Crystals, 2000 (352), p 27, the same document 2001 (360), p 81, and Liquid Crystals, 2002 (29), p 1321).    [Patent reference 1] Japanese Unexamined Patent Application, First Publication No. 2002-250924.